JP2012192491A - Grinding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for grinding a workpiece free from generation of cracks even when the workpiece is ground into a thin shape.SOLUTION: The grinding method for grinding the workpiece by a grinding wheel having a grinding stone, applies a pressure on the workpiece at least on an entrance side of the workpiece relative to the grinding stone, below an end surface of which the workpiece enters during grinding, thereby grinding the workpiece while the workpiece located on the entrance side relative to the grinding stone, is flattened relative to the workpiece located below the end surface.

Description

  The present invention relates to a grinding method for attaching a protective member to the surface of a workpiece and grinding the back surface thereof.

  A semiconductor wafer in which a number of devices such as IC and LSI are formed on the surface, and each device is partitioned by a line to be divided (street), the back surface is ground by a grinding machine and processed to a predetermined thickness. A dividing line is cut by a cutting device (dicing device) to be divided into individual devices, and the divided devices are widely used in electric devices such as mobile phones and personal computers.

  On the other hand, an optical device wafer in which a nitride semiconductor layer such as gallium nitride (GaN) is stacked on the surface and an optical device is formed in each region partitioned by the planned division lines formed in a lattice shape Are divided into individual optical devices by being irradiated with a laser beam, and the divided optical devices are widely used in electronic devices such as mobile phones and digital cameras.

  Since an optical device wafer is formed by growing a nitride semiconductor layer on a sapphire substrate suitable for the growth of an epitaxial layer, the sapphire substrate is an indispensable material for manufacturing an optical device. After the semiconductor layer is stacked, the back surface of the sapphire substrate is ground and thinned by a grinding device in order to reduce the weight, size, and improve the device characteristics of the electronic device.

  A grinding apparatus for grinding the back surface of a wafer such as a semiconductor wafer or an optical device wafer has a chuck table for holding the wafer and a grinding wheel having a grinding wheel for grinding the wafer held by the chuck table mounted rotatably. A grinding means for grinding the wafer to a desired thickness with high accuracy.

  By the way, when brittle hard materials such as sapphire or silicon nitride, lithium tantalate, and Altic, which are substrates for optical device wafers, are ground with a grinding machine, there is a problem that productivity is poor. The applicant has developed a technique for grinding an object by arranging an ultrasonic vibrator on a grinding wheel (see, for example, Japanese Patent Application Laid-Open No. 2008-23693).

JP 2008-6492 A JP 2008-23893 A

  However, if a protective tape made of an adhesive tape is attached to the surface of the optical device wafer and the sapphire substrate on the back surface of the optical device wafer is ground to reduce its thickness to 100 μm or less, and further to 50 μm or less, the sapphire substrate cracks. There is a problem that arises. The problem which arises similarly arises also in grinding of hard brittle substrates, such as a silicon carbide substrate (SiC substrate).

  Considering this cause, the work piece breaks when grinding the work piece such as a sapphire substrate. The work piece part pressed by the end face of the grinding wheel by the grinding pressure locally sinks into the protective tape. It is thought that this is because a steep step occurs between the workpiece under the end surface of the grindstone pressed by the end surface and the workpiece about to enter under the end surface of the grindstone, and the grindstone hits the step portion.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a grinding method in which cracking of the workpiece does not occur even if the workpiece is ground thinly.

  According to the present invention, there is provided a grinding method for grinding a workpiece with a grinding wheel having a grinding wheel, a protective member adhering step for adhering a protective member to the surface of the workpiece, and around a first rotation axis. A holding step for holding the surface side of the work piece to which the protection member is attached by a rotating chuck table; and a grinding wheel of the grinding wheel that rotates about a second rotation axis parallel to the first rotation axis. The workpiece is held in contact with the back surface of the workpiece that rotates around the first rotation axis while being held by the chuck table, and the grinding wheel is ground and fed in a direction approaching the workpiece. A grinding step for grinding the back surface of the workpiece, and a pressure applying step for applying pressure on the workpiece at least on the inlet side where the workpiece enters under the end surface of the grinding wheel during the grinding step. Equipped with pressure Grinding method characterized by performing grinding while applying pressure on the workpiece in a step so that the workpiece on the inlet side with respect to the grinding wheel is flattened against the workpiece under the end face Is provided.

  Preferably, in the pressure application step, a fluid equivalent to the grinding pressure of the grinding wheel is applied to the workpiece by ejecting a fluid onto the workpiece on the inlet side, so that the workpiece on the inlet side is processed. The object is flattened against the workpiece under the end face.

  According to the present invention, at the time of grinding, at least at the entrance side where the workpiece enters under the end surface of the grinding wheel, pressure is applied to the upper surface of the workpiece, so that the workpiece under the grinding wheel end surface pressed by the end surface of the grinding wheel is pressed. There is no steep step between the part of the workpiece and the workpiece that is about to enter under the end face of the grinding wheel. Accordingly, it is possible to prevent the workpiece from being cracked during grinding.

It is a perspective view of a grinding device suitable for carrying out the grinding method of the present invention. It is a surface side perspective view of an optical device wafer. It is a perspective view which shows a grinding step. It is explanatory drawing of a pressure provision area | region. It is the partial cross section side view seen from the A direction of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, an external perspective view of a grinding apparatus 2 suitable for carrying out the grinding method of the present invention is shown. Reference numeral 4 denotes a base of the grinding apparatus 2, and a column 6 is erected on the rear side of the base 4. A pair of guide rails 8 extending in the vertical direction is fixed to the column 6.

  A grinding unit (grinding means) 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The grinding unit 10 includes a spindle housing 12 and a support portion 14 that holds the spindle housing 12, and the support portion 14 is attached to a moving base 16 that moves up and down along a pair of guide rails 8. Yes.

  The grinding unit 10 includes a spindle 18 rotatably accommodated in a spindle housing 12, a motor 20 that rotationally drives the spindle 18, a wheel mount 22 fixed to the tip of the spindle 18, and a detachable attachment to the wheel mount 22. And a mounted grinding wheel 24. As shown in FIG. 3, the grinding wheel 24 includes an annular base 26 and a plurality of grinding wheels 28 arranged annularly on the outer periphery of the lower end portion of the annular base 26.

  The grinding apparatus 2 includes a grinding unit feed mechanism 34 that includes a ball screw 30 that moves the grinding unit 10 in the vertical direction along a pair of guide rails 8 and a pulse motor 32. When the pulse motor 32 is driven, the ball screw 30 rotates and the moving base 16 is moved in the vertical direction.

  Adjacent to the grinding wheel 24 of the grinding unit 10, a pressure applying nozzle 46 that applies pressure to the wafer 11 positioned at the grinding position B is disposed. In the present embodiment, high pressure water is jetted from the pressure applying nozzle 46 to apply pressure to the wafer 11 held on the chuck table 38.

  A recess 4a is formed on the upper surface of the base 4, and a chuck table mechanism 36 is disposed in the recess 4a. The chuck table mechanism 36 has a chuck table 38 and is moved in the Y-axis direction between a wafer attaching / detaching position A and a grinding position B facing the grinding unit 10 by a moving mechanism (not shown). 40 and 42 are bellows. An operation panel 44 is provided on the front side of the base 4 so that an operator of the grinding apparatus 2 can input grinding conditions and the like.

  Referring to FIG. 2, there is shown a front side perspective view of an optical device wafer 11 which is a kind of workpiece of the grinding method of the present invention. The optical device wafer 11 is configured by laminating an epitaxial layer (semiconductor layer) 15 such as gallium nitride (GaN) on a sapphire substrate 13. The optical device wafer 11 has a front surface 11a on which an epitaxial layer 15 is stacked and a back surface 11b on which the sapphire substrate 13 is exposed.

  The sapphire substrate 13 has a thickness of 430 μm, for example, and the epitaxial layer 15 has a thickness of 5 μm, for example. A plurality of optical devices 19 such as LEDs are formed in the epitaxial layer 15 by being partitioned by division lines (streets) 17 formed in a lattice pattern.

  Prior to grinding the optical device wafer 11, a protective tape 21 is attached to the surface 11a of the optical device wafer 11 in order to protect the optical device 19 on the surface 11a side of the optical device wafer 11. The protective tape 21 is configured by disposing a paste layer on one surface of a base material such as polyethylene vinyl chloride or polyolefin.

  Hereinafter, the grinding method of the present invention by the grinding apparatus 2 provided with the pressure applying nozzle 46 will be described in detail with reference to FIGS. The optical device wafer 11 is placed on the chuck table 38 positioned at the wafer attaching / detaching position A shown in FIG. 1 with the protective tape 21 facing down, and the wafer 11 is sucked and held by the chuck table 38.

  Next, a moving mechanism (not shown) of the chuck table mechanism 36 is operated to position the chuck table 38 at the grinding position B where the wafer 11 held by the chuck table 38 faces the grinding unit 10. FIG. 3 shows a state in which the wafer 11 is positioned at the grinding position.

  Although not particularly shown, the chuck table 38 is supported at three points where one side is fixed and the other two points are movable, so that the holding surface 38a of the chuck table 38 can be tilted. The movable starting point is constituted by, for example, a combination of a pulse motor and a ball screw.

  Further, the suction part of the chuck table 38 has a holding surface 38a formed in a slight mountain shape with the rotation center of the chuck table 38 as a vertex, and the difference in height between the center part of the holding surface 38a and the peripheral part. Is set to about 10 to 20 μm.

  As shown in FIG. 4, the holding surface 38a of the chuck table 38 is formed in a slight mountain shape with the center of rotation as the apex, and the chuck table 38 is adjusted to be slightly inclined so that the front side becomes higher. In addition, the grinding region G where the grinding wheel 28 contacts the back surface 11b of the optical device wafer 11 is limited to the region from the rotation center of the wafer 11 to the outer periphery, and the grinding direction is the direction from the rotation center of the wafer 11 to the outer periphery. . In FIG. 4, 29 is a rotation locus of the grinding wheel 28.

  In the grinding method of the present embodiment, the optical device wafer 11 held on the chuck table 38 by rotating the grinding wheel 24 in the direction indicated by the arrow b, for example, at 1400 rpm while rotating the chuck table 38 in the direction of the arrow a at 300 rpm, for example. The grinding wheel 24 is positioned so that the grinding wheel 28 passes through the rotation center.

  Then, the grinding unit feed mechanism 34 is driven, and the sapphire substrate 13 on the back surface 11b of the optical device wafer 11 is fed while grinding the grinding wheel 24 by a predetermined amount at a predetermined grinding feed speed (for example, 0.3 μm / s). Grind.

  At the time of this grinding, as best shown in FIG. 5, high-pressure water 50 is injected from the injection port 48 of the pressure applying nozzle 46 to the wafer 11 on the inlet side where the wafer 11 enters under the end face 28 a of the grinding wheel 28. A pressure equivalent to the grinding pressure of the grinding wheel 24 is applied, and the protective tape 21 is compressed and thinned by this pressure.

  This prevents a steep step between the back surface 11b of the wafer 11 being pressed by the end surface 28a of the grinding wheel 28 and the back surface 11b of the wafer 11 that is about to enter under the end surface 28a of the grinding wheel 28. Then, grinding is performed while the back surface 11b of the wafer 11 is flattened. In FIG. 4, P is a pressure application region by the pressure application nozzle 46.

  The pressure equivalent to the grinding pressure of the grinding wheel 24 is a pressure that does not cause a steep step between the wafer 11 below the end face of the grinding wheel 28 and the wafer 11 on the inlet side. In FIG. 5, the wafer 11 below the end face 28 a of the grinding wheel 28 and the back surface 11 b of the entrance-side wafer 11 are shown to be flat, but there may be a gentle inclination. It is sufficient that there is no steep step between the bottom of 28a and the entrance side.

  Thus, when grinding is performed while applying pressure to the wafer 11 by spraying high-pressure water with the pressure applying nozzle 46, the back surface 11b of the wafer 11 and the end surface 28a of the grinding wheel 28 where the end surface 28a of the grinding wheel 28 is pressed. Since there is no steep step between the back surface 11b of the wafer 11 that is about to enter underneath, it is possible to prevent the substrate 13 of the optical device wafer 11 from cracking during grinding.

  In the embodiment described above, high-pressure water is jetted from the pressure applying nozzle 46 to apply pressure to the wafer 11. However, the pressure applying means is not a fluid, and pressure is applied to the wafer 11 by a physically pressing means. You may make it do.

  In the above-described embodiment, the example in which the optical device wafer 19 having the optical device 19 formed on the surface is ground as the workpiece has been described. However, the surface is protected even when the workpiece having no device on the surface is ground. In the case of attaching a tape or the like for grinding, the grinding method of the present invention can be applied.

  Further, in the above-described embodiment, an example in which the grinding method of the present invention is applied to grinding of a hard brittle material such as a sapphire substrate has been described. However, the grinding method of the present invention can be similarly applied to grinding of a silicon wafer. .

  Also, instead of sticking the protective tape 21 to the front surface 11a of the optical device wafer 11, the resin is applied to the front surface 11a of the wafer 11 and cured as a protective member, and then the back surface 11b of the wafer 11 is ground. The present invention is applicable.

DESCRIPTION OF SYMBOLS 10 Grinding unit 11 Optical device wafer 13 Sapphire substrate 19 Optical device 24 Grinding wheel 28 Grinding wheel 38 Chuck table 46 Pressure application nozzle G Grinding area P Pressure application area

Claims (2)

A grinding method for grinding a workpiece with a grinding wheel having a grinding wheel,
A protective member attaching step for attaching a protective member to the surface of the workpiece; and
A holding step for holding the surface side of the work piece to which the protective member is attached with a chuck table that rotates around a first rotation axis;
An end surface of the grinding wheel of a grinding wheel that rotates about a second rotation axis parallel to the first rotation axis is held by the chuck table and contacts a back surface of a workpiece that rotates about the first rotation axis. A grinding step of grinding the back surface of the workpiece by grinding and feeding the grinding wheel in a direction approaching the workpiece,
A pressure applying step for applying pressure on the work piece at least at an inlet side where the work piece enters under the end face of the grinding wheel during the grinding step;
Applying pressure on the workpiece in the pressure applying step, and performing grinding while flattening the workpiece on the inlet side with respect to the grinding wheel with respect to the workpiece under the end surface, Grinding method.   In the pressure applying step, a fluid equivalent to the grinding pressure of the grinding wheel is applied to the work piece by ejecting a fluid onto the work piece on the inlet side, and the work piece on the inlet side is moved to the work piece. The grinding method according to claim 1, wherein the workpiece is flattened with respect to the workpiece under the end face.

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